1. Field of the Invention
The present invention relates to an optical apparatus using a lens array which is utilized for optical communications, and in particular to an optical apparatus in which optical beams emitted from respective ports of a lens array are condensed approximately on one point using a common lens.
2. Description of the Related Art
In recent years, with the speeding up of optical signals in trunk systems, an optical switching function in an optical cross-connecting apparatus or the like, is required to deal with optical signals of ultra-high speed exceeding 10, Gbps (gigabit per second). Further, with an increase in frequency of wavelength division multiplexing in a wavelength division multiplex (WDM) transmission technology, a scale of optical switching is becoming enormous.
In such a background, the development of an optical switch is now progressed, which uses a micro-tilt mirror array by the MEMS (Micro Electro Mechanical Systems) technology suitable for a large-scale optical switch (refer to a literature: “Fully provisioned 112×112, micro-mechanical optical crossconnect with 35.8, Tb/s demonstrated capacity” by D. T. Neilson et al., Optical Fiber Communications Conference (OFC 2000), Post-deadline paper PD-12, March 2000, and the pamphlet of International Patent Publication No. 00/20899).
FIG. 10 is a diagram showing a configuration example of an optical switch using a conventional lens array. Further, FIG. 11 is an enlarged diagram showing the vicinity of an A portion encircled by a dotted line in FIG. 10.
In FIG. 10 and FIG. 11, the optical switch comprises: a fiber array 111, a lens array 110 consisting of a glass block 112 and a plurality of lenses 113; and a compound lens 130 which condenses optical beams emitted from the lens array 110 on a MEMS mirror 150. In this optical switch, the optical beams emitted from the fiber array 111 are incident on the glass block 112, to travel through the glass block 112 while spreading. The optical beams passed through the glass block 112 are condensed respectively by the lenses 113 corresponding thereto, and here, become parallel beams for example. Then, the parallel beams emitted from the lenses 113 pass through the compound lens 130 to be condensed on the MEMS mirror 150. As a result, the optical beams emitted from arbitrary ports corresponding to the respective lenses 113 of the lens array 110 can be incident on different ports of the lens array 110 by tilting a mirror portion of the MEMS mirror 150, and therefore, it becomes possible to perform the changeover of optical paths.
However, in the case of attempting to realize a large scale optical switch using the conventional lens array 110 as described above, as the number of ports is increased, the variations in focal positions of the respective optical beams condensed by the compound lens 130 becomes large by an influence of aberration (for example, spherical aberration, curvature of field and the like) of each lens used for the compound lens 130. In the case where the dispersion occurs in the focal positions of the respective optical beams, a beam diameter on the MEMS mirror 150 is enlarged. Therefore, in order to absorb such an enlarged diameter, it is necessary to increase a size of the mirror portion of the MEMS mirror 150. However, if the size of the mirror portion is increased, there are caused problems in that a voltage for operating the mirror is increased, and further, in proportion to an increase in angle change of the mirror, the size of the overall optical switch is also increased.
For solving the above problems, it is considered that a lens of small aberration influence is used. However, such a lens is expense, and in the case of the compound lens 130 as shown in FIG. 10, since two lenses need to be used, there is caused a problem of resulting in a cost increase of the optical switch.